Cladding layer
This application is a continuation of application Ser. No. 362,777 filed June 7, 1989. 
    
    
     This invention relates to metal roof cladding panels of the kind which have mutually engageable edge ribs and perhaps similar intermediate stiffening ribs separated by relatively broad, essentially flat pans. 
     To reduce cost it is customary to make such panels from the thinnest steel or other base metal sheet consistent with the necessary structural strength. This does not reduce the effective life of the panels materially, which is dependent almost entirely on the corrosion resistance of the protective coating applied to the base sheet. 
     However it sometimes happens when thin panels are walked on, and this inevitably occurs when the panels are being laid, that linear marks appear in the protective and often ornamental coating, apparently produced by the flexing of the panel as a whole between the supporting battens or purlins of the roof structure. The marks are linear and extend from stiffening or edge ribs into the essentially flat pan between the ribs. Tests have shown that the marks in question are not deleterious to the functioning of the panel. Nevertheless they are objected to by many builders and other users, so requiring the replacement of essentially sound panels for cosmetic reasons. 
     An object of the present invention is to avoid the waste inherent in the replacement of such marked panels. 
     The invention achieves that object by providing, at or adjacent each junction of a rib and a pan, a bead of small cross-section, referred to as a sacrificial bead hereinafter, extending substantially parallel to the rib and projecting beyond the pan in the opposite direction to the rib. 
    
    
     By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the accompanying drawings. 
     FIG. 1 is a perspective view of a roof cladding panel according to the invention. 
     FIG. 2 is a cross-sectional view of the panel of FIG. 1. 
     FIG. 3 is an enlarged view of the part of FIG. 2 within the enclosure 3 of that figure. 
     FIG. 4 is a view similar to FIG. 3 of a second embodiment of the invention. 
    
    
     The roof panel illustrated by FIGS. 1 to 3 may be a coated steel panel and comprises a plurality of inverted channel stiffening ribs 5, inverted channel male and female edge ribs 6 and 7 and a plurality of intermediate essentially flat pans 8. The panel is supported on purlins 10. 
     Insofar as the foregoing features 5 to 8 are concerned the illustrated panel is conventional, but in accordance with the invention it also comprises a plurality of sacrificial beads 9, disposed one at each junction of a pan S and a rib 5, 6 or 7 as the case may be. The beads 9 are very much smaller than the ribs and project from the pans in the opposite direction to the ribs. 
     For example, the illustrated panel may be made from a steel sheet 0.42 mm. thick and the sacrificial beads 9 may be substantially semi-circular in cross section with an inner radius of say 1.5 mm. 
     When the panel is laid upon a batten, purlin or like support, the beads 9 project downwardly and ensure that any high pressure contact between panel and support is substantially limited to the contact between the support and the bead. 
     It has been found that when a panel according to the invention is overloaded, as by being heavily walked upon, the crests of its beads may be deformed at the edges of the supports but no further damage or marking occurs; thus it would appear that this sacrificial deformation of the bead protects the remainder of the panel. Whether that be the reason or not, it has been found that the presence of the beads has the effect of preventing the objectionable marking of the pans. Furthermore any deformation of the beads that may occur is not in itself objectionable as it does not affect the functioning of the panel and is normally not noticeable to a casual observer. 
     The FIG. 4 embodiment is the same as the above described embodiment except that its sacrificial beads 9&#39; are formed in the pans near to, but nevertheless spaced from, their junctions with the ribs. That is to say the beads 9&#39; are adjacent the junctions rather than at the junctions. It has been found that the beads may be as far as 20 mm from the ribs without affecting their effectiveness in protecting the pans from marking as aforesaid. 
     The claims defining the invention are as follows;